Method for high aspect ratio photoresist removal in pure reducing plasma

ABSTRACT

A method for removing photoresist, an oxidation layer, or both from a semiconductor substrate is disclosed. The method includes placing a substrate in a processing chamber, the processing chamber separate from a plasma chamber for generating a non-oxidizing plasma to be used in treating the substrate; generating a first non-oxidizing plasma from a first reactant gas and a first carrier gas in the plasma chamber, wherein the first non-oxidizing plasma comprises from about 10% to about 40% of the first reactant gas, wherein the first reactant gas has a flow rate of from about 100 standard cubic centimeters per minute to about 15,000 standard cubic centimeters per minute, and wherein the first carrier gas has a flow rate of from about 500 standard cubic centimeters per minute to about 20,000 standard cubic centimeters per minute; and treating the substrate by exposing the substrate to the first non-oxidizing plasma in the processing chamber.

PRIORITY CLAIMS

This application is a continuation of U.S. patent application Ser. No.14/406,256, filed Dec. 8, 2014, which claims the benefit of and priorityto the national stage entry of International Application No.PCT/US2013/050674, filed Jul. 16, 2013, which claims the benefit ofpriority of U.S. Provisional Patent Application No. 61/671,996, filedJul. 16, 2012, and U.S. Provisional Patent Application No. 61/702,865,filed Sep. 19, 2012, all of which are incorporated herein by referencefor all purposes.

FIELD

The present disclosure relates generally to the removal of photoresistand, more particularly, to a process that can remove photoresist in highaspect ratio (HAR) applications.

BACKGROUND

In the semiconductor industry, the patterns of conductors on circuitboards and the transistors on microchips are printed or etched ontosubstrates or wafers using a photoresist. For instance, many millions ofmicron-sized devices can be fabricated simultaneously and reliably onsilicon substrates via the application of a layer or multiple layers ofphotoresist. A photoresist is a polymeric coating that can changeproperties upon exposure to light and that can resist etching, ionimplantation, metal deposition, etc., to protect the substrate beneathwhere required. For example, in a situation where a chemical treatmentetches away some of the substrate, the photoresist can protect the otherregions of the substrate, after which an appropriate reagent such asplasma is utilized to remove or strip the remaining photoresist.

However, as the device feature size of integrated circuits continues tobe scaled down, removal or stripping of the photoresist becomes moredifficult, particularly in high aspect ratio (HAR) applications wherethe ratio of the length of an object to its width is greater than about25, such as greater than about 50 (i.e., when the ratio of the height ofa cavity to the width of a cavity is greater than about 25, such asgreater than about 50), or in applications where the critical dimension(CD) of the substrate becomes smaller. Further, photoresist removal withzero substrate loss while simultaneously maintaining gate materialintegrity is critical with high dose implant strip (HDIS) and descumprocesses.

One solution as it pertains to conventional oxygen-based plasmastripping is to increase power into the plasma. However, this results inoxidation damage, for example, to the metallic liner coating the insidesurfaces of HAR holes. Such oxidation, in turn, results in increasedsheet resistance and is prevalent when oxygen-rich reducing chemistry isused in conjunction with high-k metal gates (HKMGs), thus negating theelectrical advantages seen with the use of HKMGs. Further, removal ofthe oxidized layer results in severe CD change and loss of contact linerthickness, which is already thin.

Meanwhile, the use of pure reducing chemistry is well established whenstripping photoresist in the presence of metallic surfaces, but it hasintrinsically low photoresist removal rates, even at high power, andtypically, purely reducing plasmas have an order of magnitude lowerstrip rate than oxygen-based plasmas of equal power and gas feeddensity. Moreover, residual photoresist is often left at the bottom ofthe HAR holes, even when the process time is extended many times beyondthat required to strip a monolithic photoresist film of equal thickness.The different behavior is presumed to be due to the loss of reactivespecies to surface reactions along the container walls of the HAR holes,thus preventing sufficient reactant density at the surface of the holes.

Thus, a need exists for a method of removing photoresist in aneconomically feasible manner that results in minimal to zero substrateloss and does not result in the oxidation of the metallic lining in suchholes. A need also exists for a process for oxidized layer removal fromconductive materials that does not result in thickness loss.

SUMMARY

Aspects and advantages of the invention will be set forth in part in thefollowing description, or may be obvious from the description, or may belearned through practice of the invention.

One exemplary aspect of the present disclosure is directed to a methodfor removing photoresist, an oxidation layer, or both from asemiconductor substrate. The method comprises placing a substrate in aprocessing chamber, the processing chamber located downstream from aplasma chamber for generating a non-oxidizing plasma to be used intreating the substrate; generating a first non-oxidizing plasma from afirst reactant gas and a first carrier gas in the plasma chamber,wherein the first non-oxidizing plasma comprises from about 10% to about40% of the first reactant gas, wherein the first reactant gas has a flowrate of from about 0.05 standard cubic centimeters per minute per squarecentimeter of the substrate to about 12.5 standard cubic centimeters perminute per square centimeter of the substrate, and wherein the firstcarrier gas has a flow rate of from about 0.25 standard cubiccentimeters per minute per square centimeter of the substrate to about15 standard cubic centimeters per minute per square centimeter of thesubstrate; and treating the substrate by exposing the substrate to thefirst non-oxidizing plasma in the processing chamber.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdescription and appended claims. The accompanying drawings, which areincorporated in and constitute a part of this specification, illustrateembodiments of the invention and, together with the description, serveto explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure, including the best mode, to one ofordinary skill in the art, is set forth more particularly in theremainder of the specification, including reference to the accompanyingfigures, in which:

FIG. 1 depicts a plasma reactor that can be used in the methods embodiedby the present disclosure;

FIG. 2 depicts a flow diagram of a method for removing photoresist asembodied by the present disclosure;

FIG. 3 is a graph depicting the normalized silicon loss based on thepercentage of H₂ content in a plasma treatment and the aspect ratio;

FIG. 4 is a graph depicting the effect of the H₂ percentage in anH₂/Argon plasma blend on the photoresist removal rate;

FIG. 5 is a graph depicting the effect of a NH₃ only plasma treatment onthe sheet resistance (R_(s)) of titanium nitride (TiN) oxidized surfaceover time;

FIG. 6(a) is a graph depicting the amount of TiN loss in Angstroms basedon the plasma treatment to which the TiN surface was exposed;

FIG. 6(b) is another graph depicting the amount of TiN loss in Angstromsbased on the plasma treatment to which the TiN surface was exposed; and

FIG. 7 is a graph depicting the effect of various treatments on thesheet resistance (R_(s)) of titanium nitride (TiN) surface over time.

DETAILED DESCRIPTION

Reference now will be made in detail to embodiments of the invention,one or more examples of which are illustrated in the drawings. Eachexample is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that various modifications and variations can be madein the present invention without departing from the scope or spirit ofthe invention. For instance, features illustrated or described as partof one embodiment can be used with another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventioncovers such modifications and variations as come within the scope of theappended claims and their equivalents.

Generally, the present disclosure is directed to a method of removingphotoresist, an oxidized layer, or both from a substrate using anon-oxidizing plasma chemistry supplied via a downstream inductivelycoupled plasma source. Inductive plasma sources are often used forplasma processing to produce high density plasma and reactive speciesfor processing wafers. For instance, inductive plasma sources can easilyproduce high density plasma using standard 13.56 MHz and lower frequencypower generators. Inductive plasma sources combined with RF bias havealso been used in etchers, for example, to provide independent controlof ion energy and ion flux to the wafer.

For certain plasma processes such as processes for photoresist oroxidized layer removal, it is generally not desirable to expose thesemiconductor wafers directly to the plasma. The plasma is formedremotely (e.g., downstream) from the processing chamber and desiredparticles are channeled to the semiconductor wafer or substrate, forexample, through a grid that is transparent to neutral particles and nottransparent to the plasma. Such processes can require high RF power(e.g., up to about 6 kilowatts (kW)) and in some cases high gas flows(e.g., about 20,000 standard cubic centimeters per minute (sccm)) andhigh pressure (e.g., up to about 5000 milliTorr (mTorr)), when treatingtwo substrates each having an overall diameter of about 300 millimeters(mm).

It is to be understood, however, that when only a single substrate istreated, the flow rate can generally be half of the flow rate requiredfor treating two substrates. Further, it is also to be understood thatsubstrates having diameters of from about 100 mm to about 500 mm, suchas from about 200 mm to about 450 mm, can also be treated using themethods embodied by the present disclosure, where the RF power and flowrates can be adjusted based on the surface area of the substrate. Forinstance, when a single 200 mm diameter substrate is treated instead ofa single 300 mm diameter substrate, based on the ratio of the surfacearea of the substrates, the flow rates utilized should be about 0.44times of the flow rates used for a 300 mm substrate, while when a 450 mmdiameter substrate is treated, the flow rates utilized should be about2.25 times the flow rates used for a 300 mm substrate.

FIG. 1 depicts a plasma reactor 100 that can be used in the methodsembodied by the present disclosure, although it is to be understood thatany other suitable reactor having a downstream inductively coupledplasma source can also be utilized. As illustrated, plasma reactor 100includes a processing chamber 110 and a plasma chamber 120 that isseparate from the processing chamber 110. Processing chamber 110includes a substrate holder or pedestal 112 operable to hold a substrate114 from which photoresist is to be removed, such as a semiconductorwafer. An inductive plasma is generated in plasma chamber 120 (i.e.,plasma generation region) and desired particles are channeled from theplasma chamber 120 to the surface of substrate 114 through holesprovided in a grid 116 that separates the plasma chamber 120 from theprocessing chamber 110 (i.e., downstream region).

The plasma chamber 120 includes a dielectric side wall 122 and a ceiling124. The dielectric side wall 122 and ceiling 124 define a plasmachamber interior 125. Dielectric side wall 122 can be formed from anydielectric material, such as quartz. An induction coil 130 is disposedadjacent the dielectric side wall 122 about the plasma chamber 120. Theinduction coil 130 is coupled to an RF power generator 134 through asuitable matching network 132. Reactant and carrier gases can beprovided to the chamber interior from gas supply 150 and annular gasdistribution channel 151. When the induction coil 130 is energized withRF power from the RF power generator 134, a substantially inductiveplasma is induced in the plasma chamber 120. In a particular embodiment,the plasma reactor 100 can include an optional faraday shield 128 toreduce capacitive coupling of the induction coil 130 to the plasma.

To increase efficiency, the plasma reactor 100 can optionally include agas injection insert 140 disposed in the chamber interior 125. The gasinjection insert 140 can be removably inserted into the chamber interior125 or can be a fixed part of the plasma chamber 120. In someembodiments, the gas injection insert can define a gas injection channelproximate the side wall of the plasma chamber. The gas injection channelcan feed the process gas into the chamber interior proximate theinduction coil and into an active region defined by the gas injectioninsert and side wall. The active region provides a confined regionwithin the plasma chamber interior for active heating of electrons. Thenarrow gas injection channel prevents plasma spreading from the chamberinterior into the gas channel. The gas injection insert forces theprocess gas to be passed through the active region where electrons areactively heated.

Regardless of the type of downstream inductively coupled plasma sourceutilized in the methods of the present disclosure, the present inventorshave discovered that one or more non-oxidizing plasma treatments withone or more plasma chemistries can be carried out on a semiconductorsubstrate to increase the amount of photoresist removed from thesubstrate while at the same time minimizing the amount of oxidation andchange in critical dimension (CD). Generally, the plasmas used in thetreatment processes of the present disclosure are non-oxidizing. Themethods of the present disclosure allow for photoresist removal and theprevention or removal of surface oxidation. For instance, in oneembodiment, a method is described that can be carried out on siliconsurfaces that must not be oxidized during the photoresist strippingprocess. The method can also be carried out on HAR trenches or any othercavity with a lateral dimension that is small relative to the depth ofthe cavity in the substrate. In other embodiments, the presentdisclosure describes a method that includes a main plasma treatment toremove photoresist, followed by a second plasma treatment to removeoxidation while minimizing the amount of substrate loss or modification.

Regardless of the number and specific type of plasma treatments, the oneor more plasmas used in treating a substrate can each include a reactantgas and a carrier gas, which are both free of oxygen. In certainembodiments, the reactant gas can include hydrogen, while the carriergas can be free of hydrogen. For instance, the reactant gas can behydrogen (H₂), ammonia (NH₃), or methane (CH₄). In other embodiments,the reactant gas can be free of both oxygen and nitrogen. For instance,the reactant gas can be H₂ or CH₄. Meanwhile, the carrier gas caninclude an inert gas. In certain embodiments, the inert gas can includenitrogen (N₂) or noble gases such as argon (Ar) or helium (He), orcombinations thereof. In other embodiments, however, the carrier gas canbe an inert gas that is free of nitrogen, such as one of the noblegases. Generally, the reactant gas can be present in an amount that isfrom about 10% to about 40% of the total gas volume of the reactant gasand the carrier gas, such as from about 15% to about 30% of the totalgas volume of the reactant gas and the carrier gas, such as from about20% to about 25% of the total gas volume of the reactant gas and thecarrier gas. In one particular embodiment, the reactant gas can bepresent in an amount that is about 20% of the total gas volume of thereactant gas and the carrier gas.

The reactant gas and the carrier gas can be introduced into the plasmageneration chamber and processing chamber at various flow rates. Forinstance, when two 300 mm substrates are being treated, the reactant gascan have a flow rate of from about 100 to about 15,000 sccm, such asfrom about 1,000 sccm to about 10,000 sccm, such as from about 2,000sccm to about 5,000 sccm. Meanwhile, the carrier gas can have a flowrate of from about 500 sccm to about 20,000 sccm, such as from about5,000 sccm to about 17,500 sccm, such as from about 10,000 sccm to about15,000 sccm. On the other hand, when only a single 300 mm substrate isbeing treated, the reactant gas can have a flow rate of from about 50 toabout 7,500 sccm, such as from about 500 to about 5,000 sccm, such asfrom about 1,000 to about 2,500 sccm. Meanwhile, when only a single 300mm substrate is being treated, the carrier gas can have a flow rate offrom about 250 sccm to about 10,000 sccm, such as from about 2,500 sccmto about 8,750 sccm, such as from about 5,000 sccm to about 7,500 sccm.

Based on the surface area of the substrate (e.g., a single 300 mmdiameter substrate having a surface area of about 706.5 centimeterssquared (cm²), this corresponds with a reactant gas that has a flow rateof from about 0.07 sccm per cm² of substrate to about 10.75 sccm per cm²of substrate, such as from about 0.7 sccm per cm² of substrate to about7.25 sccm per cm² of substrate, such as from about 1.25 to about 3.5sccm per cm² of substrate. Meanwhile, this corresponds with a carriergas that has a flow rate of from about 0.35 sccm per cm² of substrate toabout 14.25 sccm per cm² of substrate, such as from about 3.5 sccm percm² of substrate to about 12.5 sccm per cm² of substrate, such as fromabout 7.0 sccm per cm² of substrate to about 10.75 sccm per cm² ofsubstrate. Using the flow rates in sccm per cm² of substrate, then theflow rates in sccm for substrates having any diameter can be determinedby multiplying the sccm per cm² of substrate rate by the surface area ofthe substrate.

For instance, when a single, 200 mm substrate is treated, the reactantgas can have a flow rate of from about 20 to about 3,300 sccm, such asfrom about 220 to about 2,200 sccm, such as from about 440 to about1,100 sccm. On the other hand, the carrier gas can have a flow rate offrom about 110 to about 4,400 sccm, such as from about 1,100 sccm toabout 3850 sccm, such as from about 2,200 sccm to about 3,300 sccm.

Meanwhile, when a single, 450 mm substrate is treated, the reactant gascan have a flow rate of from about 110 sccm to about 16,875 sccm, suchas from about 1,125 sccm to about 11,250 sccm, such as from about 2,250sccm to about 5,625 sccm. On the other hand, the carrier gas can have aflow rate of from about 560 sccm to about 22,500 sccm, such as fromabout 5,625 sccm to about 19,675 sccm, such as from about 11,250 sccm toabout 16,875 sccm.

Further, photoresist removal can be carried out at varying temperatureand power levels. For example, the temperature during photoresistremoval can range from about 150° C. to about 350° C., such as fromabout 200° C. to about 325° C., such as from about 250° C. to about 300°C. In one particular embodiment, the photoresist removal can be carriedout at a temperature of about 275° C. Additionally, the RF source powerfor treating 300 mm diameter substrates can range from about 1 kW toabout 6 kW, such as from about 1.5 kW to about 5.5 kW, such as fromabout 2 kW to about 5 kW. Meanwhile, it is to be understood that thesource power can be adjusted up or down based on the surface area of thesubstrate to be treated in the same manner as discussed above for thereactant and carrier gas flow rates. Thus, for treating a substrate, thesource power can range from about 0.4 kW to about 13.5 kW, such as fromabout 0.6 kW to about 12.5 kW, such as from about 0.8 kW to about 11.5kW, when the substrate.

Moreover, photoresist removal can be carried out at varying pressures.For instance, the pressure can range from about 100 mTorr to about 4,000mTorr, such as from about 250 mTorr to about 3,500 mTorr, such as fromabout 500 mTorr to about 2,500 mTorr, such as from about 750 mTorr toabout 1,000 mTorr. In one particular embodiment, the pressure can beabout 900 mTorr.

In addition, during photoresist removal, the substrate from which thephotoresist is to be removed can be treated for a specified time basedon the CD and aspect ratio of any holes, cavities, or channels in thesubstrate to be treated. For instance, the processing time can rangefrom about 10 seconds to about 180 seconds, such as from about 20seconds to about 90 seconds, such as from about 30 seconds to about 60seconds. In one particular embodiment, the processing time can be about45 seconds, such as when the substrate to be treated has holes,cavities, or channels having an aspect ratio of greater than 50 and acritical dimension less than 0.03 micrometers.

The present inventors have discovered certain processing conditionsbased on the combinations of reactant gases and carrier gases uses informing the plasma. For example, when the reactant gas is either 20% NH₃or 20% H₂ and the carrier gas is N₂, the substrate can be treated forabout 45 seconds at a temperature of about 275° C., a pressure of about900 mTorr, and a source power of 5 kW, where the reactant gas has a flowrate of 3,000 sccm and the carrier gas has a flow rate of 12,000 sccm.Meanwhile, when the reactant gas is either 20% H₂ and the carrier gas isAr, the substrate can be treated for about 45 seconds at a temperatureof about 275° C., a pressure of about 900 mTorr, and a source power of 5kW, where the reactant gas has a flow rate of 2,500 sccm and the carriergas has a flow rate of 10,000 sccm.

After a substrate has been treated one or more times with a plasmagenerated under the conditions discussed above to remove photoresist,the substrate can be evaluated to determine its increase in sheetresistance. The larger the percent increase in sheet resistancecoincides with a larger amount of oxidation or damage to the substrateafter photoresist strip removal. As such, it is more desirable to have alower percent change in sheet resistance than a higher percent change insheet resistance. After photoresist is removed from a substrateaccording to the method of the present claims, the sheet resistancegenerally changes by only about 5% or less. For instance, the change insheet resistance can range from about 0.1% to about 4%, such as fromabout 0.5% to about 4%, such as from about 1% to about 3%. Further, thesubstrate, after one or more plasma treatments, can have a decrease inthickness that is less than about 0.75 nanometers. In some embodiments,the decrease in thickness ranges from about 0.05 nanometers to about 0.6nanometers, such as from about 0.075 nanometers to about 0.5 nanometers,such as from about 0.1 nanometers to about 0.4 nanometers, such as lessthan about 0.3 nanometers. These minimal changes indicate that themethod of the present disclosure can efficiently remove photoresist andpossible oxidation layers without damaging or removing material from thesubstrate itself.

The photoresist and oxidation removal methods defined by the parametersdiscussed above can be carried out on numerous substrate materials. Forinstance, the process can be applied to a HAR substrate where thesubstrate has holes, cavities, or channels having an aspect ratio(height of cavity/diameter of cavity) that is greater than 50 and havinga diameter as small as about 0.03 micrometers. Traditionally, it isdifficult to remove photoresist from such holes, cavities, or channels.However, as shown in the examples below and in contrast to what would beexpected, by combining a reactant gas (i.e., a hydrogen-containing gas)with a separate, inert carrier gas, the present inventors have foundthat more effective photoresist removal from HAR holes can result whencompared to removal via the hydrogen-containing reactant gas alone.Further, using the reactant gas and carrier gas method of the presentcan prevent damage to oxygen-sensitive HAR holes while still remainingefficient.

The photoresist removal method of the present disclosure can also beextended to other applications where surface oxidation is a concern andshould be prevented and where high photoresist removal is needed. Forinstance, the method of the present disclosure can be used in thepresence of silicon surfaces that must not be oxidized by thephotoresist stripping process. Other conductive materials on which themethod of the present disclosure can be applied include titanium nitride(TiN), tantalum nitride (TaN), copper (Cu), tungsten (W), or anymaterial having the formula M_(x)N_(y), where M is a metal, x and y arepositive integers, and N is nitrogen, as such materials are alsosensitive to oxygen exposure. The method can also be used for HDISphotoresist strip and photoresist strip on metal where metal material isexposed during photoresist removal or descum photoresist removal.Further, the method can be used to remove an oxidation layer onconductive materials with minimal modification (i.e., little change inthickness) of the material.

The method by which photoresist and oxidation can be removed can becarried out in the plasma reactor discussed above in reference to FIG. 1or with any other suitable plasma reactor that may have an alternativelyshaped gas injection insert. Generally, as shown in the block diagram ofFIG. 2, a method 200 for removing photoresist, an oxidation layer, orboth from a semiconductor substrate can include placing a substrate in aprocessing chamber of a plasma reactor that is located downstream from aplasma chamber (201), generating a first non-oxidizing plasma from afirst reactant gas and a first carrier gas in the plasma chamber of theplasma reactor (202), and treating the substrate by exposing thesubstrate to the first non-oxidizing plasma in the processing chamber(203). The first non-oxidizing plasma can include from about 10% toabout 40% of the first reactant gas. Further, the first reactant gas canhave a flow rate of from about 100 standard cubic centimeters per minuteto about 15,000 standard cubic centimeters per minute and the firstcarrier gas can have a flow rate of from about 500 standard cubiccentimeters per minute to about 20,000 standard cubic centimeters perminute.

The method can further include a second plasma treatment step where asecond non-oxidizing plasma can be generated from a second reactant gasand a second carrier gas in the plasma chamber (204). The secondnon-oxidizing plasma can also include from about 10% to about 40% of thesecond reactant gas. Further, the second reactant gas can have a flowrate of from about 100 standard cubic centimeters per minute to about15,000 standard cubic centimeters per minute, and the second carrier gascan have a flow rate of from about 500 standard cubic centimeters perminute to about 20,000 standard cubic centimeters per minute. In thesecond plasma treatment step, the substrate can be treated by exposingthe substrate to the second non-oxidizing plasma in the processingchamber (205).

Aspects of the present disclosure may be better understood by referenceto the following examples, which refer to FIGS. 3-7 and demonstrate theeffectiveness of the photo resist removal methods discussed above.

Example 1

Using N₂ as the carrier gas and H₂ as the reactant gas, where thepercentage of H₂ was varied based of the total volume of the carrier gasand reactant gas combined, a silicon substrate having a normalizedaspect ratio of about 1.5 was treated in a plasma reactor having aseparate plasma generation chamber and processing chamber. A pair of 300mm silicon substrates were placed in the processing chamber and werethen treated with plasma formed in the plasma generation chamber. Theamount of H₂ utilized ranged from 0% to about 80%. As shown in FIG. 3,the amount of silicon loss increased as the amount of H₂ reactant gas inthe H₂/N₂ mixture increased beyond 20%.

Example 2

Next, the type of plasma reactor, RF power, and reactant/carrier gascompositions were varied to determine the effect on the ability of themethod of the present disclosure to successfully remove photoresist froma pair of 300 mm substrates. The carrier gas in each scenario was N₂,while the reactant gas was either H₂ or NH₃ at a volume of 20% of thetotal gas volume. One of the plasma reactors utilized is shown in FIG. 1and is discussed in detail above and had a wall-type gas injectioninsert (see insert 140 in FIG. 1). The other plasma reactor utilized hasa gas injection insert that is a tube as discussed above. The substrateswere HAR contact containers having an aspect ratio greater than 50 and aCD less than 0.03 micrometers. For the scenarios tested, the 50:1 aspectratio holes were successfully cleaned at a commercially viable ratewithout degrading the metal liner, except some residue remained when thegas injection insert of the plasma source was a tube, 3 kW RF power wasused, and the reactant gas was H₂. The results are summarized below inTable 1.

TABLE 1 Plasma Source/RF Power Source Reactant/ FIG. 1 FIG. 1 CarrierGas Tube/5 kW Tube/3 kW Wall/5 kW Wall/3 kW 20% H₂/N₂ Clean ResidueClean Clean 20% NH₃/N₂ — — — Clean

Example 3

Next, although 20% H₂/N₂ and 20% NH₃/N₂ were shown in Examples 1 and 2above to be useful in removing photoresist from HAR contact containers,such Examples do not show the effect of such plasma treatments on thethickness of a TiN substrates. Thus, in Example 3, TiN, which iscommonly used as a contact liner, was exposed during photoresist removalusing 20% NH₃/N₂ as the reactant gas/carrier gas mixture. As shown belowin Table 2, the photoresist removal caused TiN thickness losses greaterthan the stringent specification of less than 0.3 nanometers.

TABLE 2 Process TiN Loss (nanometers) Control 0.317 20% NH₃/N₂ 0.732 20%NH₃/N₂ 0.666

Example 4

Next, because removing photoresist from TiN with 20% NH₃/N₂ resulted inTiN loss greater than 0.3 nanometers thick, photoresist removal was thencarried out using 20% H₂ with Ar instead and at various power levels.The results are summarized in Table 3 below and FIG. 4. FIG. 4 showsthat the rate of photoresist removal with H₂ and Ar is dependent on thepercentage of volume of H₂ based on the total volume of the H₂ and Ar.As shown in FIG. 4, photoresist removal is most efficient at an H₂percentage of 20%, with the efficiency dropping off at 10% and 30% H₂,as measured by the photoresist ash rate. For instance, the ash rate for20% H₂ was about 7600 Angstroms/minute, while the rate for 10% H₂ wasabout 6600 Angstroms/minute and the rate for 30% H₂ was about 6500Angstroms/minute. Meanwhile, Table 3 shows that photoresist removal with20% H₂/Ar limits the TiN loss to less than 0.3 nanometers when the powerwas less than 5 kW.

TABLE 3 Process TiN Loss (nanometers) 20% H₂/Ar; 5 kW 0.322 20% H₂/Ar; 4kW 0.196 20% H₂/Ar; 3 kW 0.149

Example 5

Next, the ability of the process of the present disclosure to remove anoxidized layer from a conductive material was examined. First, pure NH₃was used to treat a pair of 300 mm conductive substrates containing TiN,where an oxidized layer was present due to a dry plasma treatment of 40%NH₃/O₂. As shown in FIG. 5, after treatment with pure NH₃ for about 60seconds, the % change in sheet resistance (R_(S)) of an oxidized TiNsubstrate was only about 1% after being about 5% at 0 seconds,indicating the NH₃ was able to remove some of the oxidation from the TiNsubstrate. Meanwhile, as summarized in Table 4 below, various reducingchemistries and their effect on TiN loss were tested. As shown, anO₂-rich reducing chemistry (10% NH₃/O₂) resulted in about a 1.0nanometer (10 Angstrom) loss when followed by an NH₃ post-treatment,compared to a TiN loss of only about 0.4 nanometers for the control.

TABLE 4 Process TiN Loss (nanometers) Control 0.442 10% NH₃O₂ + NH₃ Post0.995

Example 6

In Example 6, various oxidation layer removal steps were compared. Theresults are summarized in FIGS. 6(a) and 6(b) and Table 5. As shown inFIGS. 6(a) and 6(b), a controlled sequence, hydrofluoric acid (HF) dipas a wet oxide removal step shows 0.4 nanometer (4 Angstrom) losses ofTiN within hours. After this initial HF dip to remove the native oxide,the film thickness for each substrate was measured, and then variousother treatments for oxide removal were carried out, as listed below inTable 5, followed by a second HF dip, after which the thicknesses of thesubstrates were measured so that the TiN loss for the substrates couldbe compared. Using the HF dip as the baseline, further treatmentincluded exposure of the TiN substrates to various plasmas for 60seconds at 3 kW RF power. As shown, the least TiN loss (less than about0.3 nanometers/3 Angstroms) was observed when the TiN substrates weretreated with Ar combined with H₂, He, or both.

TABLE 5 Process TiN Loss (nanometers) HF dip only 0.4 Ar/H₂ (20%) 0.262Ar/N₂ (20%) 0.304 Ar/(N₂/H₂ (20%)) 20% 0.427 Ar/NH₃ (20%) 0.359 NH₃ 0.38Ar/He (5%) 0.275 Ar/He (20%)/H₂ (20%) 0.261 He/Ar (20%)/H₂ (20%) 0.251He (20%)/Ar 0.454 He/H₂ (20%) 0.377

Example 7

In Example 7, the effects of applying NH₃ only during various points inthe oxidation layer removal process from a TiN film were compared.Depending on the sample, the NH₃ was applied at various points in theprocess: (1) strike, (2) strike and post, and (3) pre-plasma, strike,and post 40% NH₃/O₂ dry plasma treatment. The pre-plasma step refers tothe point in the process where gas is flowing and temperature/pressureare being controlled, but no RF power has been introduced to create aplasma. This step is generally carried out to stabilize the chamberenvironment after loading the substrate and can equilibrate thesubstrate temperature. The strike step refers to point of plasmaignition. Meanwhile, the post-process step refers to the point in theprocess where chamber pressure is regulated to the level required forsubstrate exchange and where any reactive gases are purged out prior toopening the chamber door.

In FIG. 7, POR refers to the control, which includes 40% NH₃/O₂ dryplasma treatment. The reduction in oxidation was measured in terms ofpercent change in sheet resistance, with the lowest percent changereflecting the highest removal of oxidation from the film with minimalmaterial modification. The results are shown in FIG. 7. As shown, theaddition of pre and post processing treatment steps where NH₃ wasapplied significantly reduced the percent change in sheet resistance.The NH₃ strike plus pre and post treatment combination was shown to bethe most effective at minimizing material modification. However, itshould be understood that the same strategy can be used with otherplasmas such as N₂/H₂, Ar, He, H₂, CH₄, etc.

Example 8

Next, a combined main stripping process step with a post treatment stepwas carried out on a TiN liner having holes with an aspect ratio of 50and a diameter of 0.03 micrometers using a main photoresist removalprocess with 20% NH₃/N₂ (a first non-oxidizing plasma treatment),followed by a 20% H₂/Ar post-main strip treatment (a secondnon-oxidizing plasma treatment). This was then compared to a 20% H₂/Artreatment alone. As shown in Table 6 below, these treatments resulted inTiN loss of about 0.3 nanometers or less.

TABLE 6 Process and Time TiN Loss (nanometers) 20% H₂/Ar (60 s) 0.26220% NH₃/N₂ + 20% H₂/Ar (60 s) 0.303 20% NH₃/N₂ + 20% H₂/Ar (180 s) 0.288

These and other modifications and variations to the present inventionmay be practiced by those of ordinary skill in the art, withoutdeparting from the spirit and scope of the present invention, which ismore particularly set forth in the appended claims. In addition, itshould be understood that aspects of the various embodiments may beinterchanged both in whole or in part. Furthermore, those of ordinaryskill in the art will appreciate that the foregoing description is byway of example only, and is not intended to limit the invention sofurther described in such appended claims.

What is claimed is:
 1. A method for processing a substrate comprising a TiN liner having holes with an aspect ratio of at least 50 and a photoresist layer, the method comprising: placing the substrate in a processing chamber, the processing chamber located downstream from a plasma chamber; generating a first non-oxidizing plasma from a first process gas in the plasma chamber, the first process gas comprising a first carrier gas and a first reactant gas, wherein the first process gas comprises from about 10% to about 40% of the first reactant gas, wherein the first reactant gas comprises NH₃ and the first carrier gas comprises N₂; exposing the substrate to species of the first non-oxidizing plasma in the processing chamber to implement a strip process for removal of at least a portion of the photoresist layer; generating a second non-oxidizing plasma from a second process gas in the plasma chamber, the second process gas comprising a second carrier gas and a second reactant gas, wherein the second process gas comprises from about 10% to about 40% of the second reactant gas, wherein the second reactant gas comprises H₂ and the second carrier gas comprises Ar; exposing the substrate to species of the second non-oxidizing plasma in the processing chamber to implement a post-strip treatment process on the substrate.
 2. The method of claim 1, wherein the first process gas comprises about 20% of the first reactant gas.
 3. The method of claim 1, wherein the second process gas comprises about 20% of the second reactant gas.
 4. The method of claim 1, wherein the plasma chamber comprises a dielectric sidewall.
 5. The method of claim 4, wherein an induction coil is disposed adjacent the dielectric sidewall.
 6. The method of claim 1, wherein the method is carried out at a source power ranging from about 0.4 kilowatts to about 13.5 kilowatts.
 7. The method of claim 1, wherein the method is carried out at a pressure ranging from about 100 milliTorr to about 4000 milliTorr.
 8. The method of claim 1, wherein the substrate is treated at a temperature ranging from about 150° C. to about 350° C.
 9. The method of claim 1, wherein the substrate is treated by exposing the substrate to the species of the first non-oxidizing plasma for a time period ranging from about 10 seconds to about 180 seconds.
 10. The method of claim 1, wherein the substrate has a diameter of from about 100 millimeters to about 500 millimeters.
 11. The method of claim 1, wherein the strip process comprises a photoresist removal process.
 12. The method of claim 1, wherein the species of the first non-oxidizing plasma comprise neutral particles and the species of the second non-oxidizing plasma comprise neutral particles. 